The overall goal of the research is to further elucidate the cognitive deficit responsible for the reading and spelling difficulties of individuals with familial dyslexia. This project is unique among studies of dyslexia in that these dyslexics are homogeneous with respect to etiology: they have an autosomal dominant form of familial dyslexia which is linked to chromosome 15. Thus they are likely to be both more homogeneous and specific in their phenotype than other dyslexic populations. The proposed research extends our earlier work on the cognitive phenotype in this population in two areas: the underlying neurolinguistic deficit or deficits and the cognitive strategies used in reading and spelling. In the former area, our earlier work found possible deficits in phoneme discrimination or segmentation skills, lexical retrieval, and phonological memory. The proposed research will attempt to disentangle experimentally these closely related skills. In the second area, we found their oral reading was much more impaired than reading comprehension, and that their written spelling was characterized by problems with both phonetic correspondences and more subtle orthographic rules and regularities. The proposed research will systematically test both the strategy they use to gain lexical access in reading and their orthographic "competence" using priming, stroop, and letter search paradigms employing carefully selected words and non-words. Since our previous work suggests that aspects of the cognitive phenotype changes with development, the proposed research will also attempt to further specify the basic of these developmental changes. Thus, we will study cross-sectionally three subject groups: familial dyslexics, their unaffected family members, and non-familial dyslexics, at three developmental ages: 8 to 10 years, 12 to 14 years, and adulthood. A final phase will involve a three year longitudinal study of the 8 to 10 year olds in all three subject groups.